1. Field of the Invention
The present invention relates to a power cable arrangement structure in an electronic apparatus such as a facsimile machine, printer, copying machine or image scanner.
2. Description of the Related Art
A facsimile machine is an electronic apparatus used for transmitting and receiving image data to and from a remote facsimile machine through a telephone line. For this purpose, the facsimile machine incorporates a modem and a network control unit (NCU) provided with a transformer. The modem and the NCU may be disposed on a power circuit board. Further, the facsimile machine also incorporates a printhead mounted on a signal processing circuit board which receives and processes the image data from the modem or an image reading unit.
The power circuit board of the facsimile machine is connected to a commercial power outlet of e.g. AC 100V and to the signal processing circuit board. The power supply circuit on the power circuit board converts the AC power voltage to a DC power voltage of 6-24V for use on the signal processing circuit board. The electrical connection between the power circuit board and the signal processing circuit board is established by a suitable number of power cables which include at least one power supply cable for supplying the DC power and at least one power return cable for passage of return current to the power circuit board.
Due to the limitation of available space within the facsimile machine, the power cables are inevitably arranged to extend near the transformer if the power cables are connected to the signal processing circuit board. Further, a relatively large current flows through the power cables, so that a relatively strong magnetic field is concentrically around the respective power cables. Thus, if the power supply through the power cables is switched on and off, the intensity of the magnetic field varies with time due to electromagnetic induction. As a result, the nearby transformer and/or the nearby circuit boards are likely to suffer noises.
One way to solve this problem is to enclose the transformer in a magnetic shield conductor and/or to interpose a magnetic shield conductor plate between the power cables and the nearby circuit board. However, such a solution is disadvantageous in that an additional insulation is required for avoiding electrical shorting between the magnetic shield conductor and the transformer (and/or the nearby circuit board), which may lead to a structural complication of the electronic apparatus and an increase in the required number of components while also increasing the assembly steps.
Another solution is to surround the outer insulation sheath of each power cable with a copper wire net which is grounded for magnetic shielding. The use of the grounding wire net will result in an added cost. Further, there is also additional steps of surrounding the power cable with the copper wire net and of grounding the wire net.